Liquid crystal alignment structures and optical devices containing same

ABSTRACT

An alignment structure useful in a liquid crystal display device comprising a substrate having disposed thereon an oriented film of a lyotropic nematic liquid crystalline material. Particularly useful lyotropic materials include a class of nematic liquid crystalline compounds known as chromonics. The substrates can be made by coating the lyotropic liquid crystal material onto the substrate to provide an oriented film of the lyotropic material. The alignment structure can also include one or more polarizing dyes or other additives and can thus be made to perform polarizing, retarding and/or color filtering functions in addition to alignment and orientation functions. Optical devices containing such alignment structures and methods of making such devices are also described.

This is a continuation-in-part of application Ser. No. 09/439,190 filedNov. 12, 1999 abandoned.

FIELD OF THE INVENTION

In one aspect, the present invention relates to structures, includingalignment films and alignment substrates useful in liquid crystaldisplays. In another aspect, the invention relates to display devicesand other optical devices that utilize liquid crystal alignment films orsubstrates therein.

BACKGROUND OF THE INVENTION

A common liquid crystal display, or “LCD,” contains an array oftwo-dimensional picture elements, or pixels. Although each pixel may,and customarily does, contain numerous optical elements, each comprisesa liquid crystal cell. A liquid crystal cell generally comprises aliquid crystal material maintained between a pair of transparentsubstrates, and those substrates most commonly are made of glass or apolymeric material such as polyimide. Interposed between the liquidcrystal material and the substrates are electrodes electricallyconnected to an outside signal device that, when electrically active,alter the state of the liquid crystal material. Such liquid crystalcells find application not only in displays, but also in other opticaldevices, including optical communication devices and other opticalprocessing equipment.

In a liquid crystal cell, the molecules of liquid crystal material arealigned, or oriented, in a preferred direction along each of thesubstrates within the cell. Normally, this alignment is accomplishedthrough the use of an alignment structure layer. Alignment layersgenerally are glass substrates or polymeric films, typically polyimides,that are mechanically rubbed in a single direction to impart anorientating effect on the liquid crystals with which they contact. Theoptical activity of the liquid crystal cell is in part a function of therelative orientation of the liquid crystals at the surface of each ofthe substrates and the ordered change in direction of the crystalsbetween the substrates.

Such conventional alignment layers suffer myriad drawbacks. For example,the high temperatures necessary to process of many useful polymericsubstrates prevent the incorporation of temperature-sensitive additivessuch as color dyes into the alignment structures. Also, the conventionalrubbing, washing and drying steps used in manufacture of the layer filmsand substrates can be slow, expensive and introduce gross defects andlow yields.

SUMMARY OF THE INVENTION

Briefly, in one aspect, the present invention provides an alignmentstructure useful in a liquid crystal display device that comprises asubstrate having disposed thereon an oriented film or layer of alyotropic liquid crystalline material. Particularly useful lyotropicliquid crystalline materials include a class of compounds known aschromonics. The structures of the invention can be made by coating theliquid crystalline material onto a substrate to provide an oriented filmof the lyotropic material. The alignment substrates can also include oneor more dyes or other additives and can thus, in addition to alignmentand orientation, be made to perform polarizing, retarding and/or colorfiltering functions. The alignment structures can also be made with oneor more additional layers, such as, for example, cholesteric retarders,non-optical polymers, etc.

In another aspect the invention provides optical devices. The opticaldevices include at least one liquid crystal material disposed betweentwo substrates, wherein at least one of the substrates have disposedthereon an oriented film of a lyotropic liquid crystalline material. Inother aspects, the invention provides methods of making such alignmentstructures and optical devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a scanning electron microscopic (SEM) image of the orderedsurface of an alignment structure according to the invention.

FIG. 2 is a schematic view of a liquid crystal cell according to oneaspect of the invention.

FIG. 3 is a schematic view of an alignment structure that incorporatesan ordered layer of lyotropic liquid crystal material according to theinvention.

FIG. 4 is a schematic cross-sectional view of a two-polarizer liquidcrystal display according to one aspect of the invention.

FIG. 5 is a schematic cross-sectional view of a color liquid crystaldisplay according to one aspect of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In their most essential respect, the liquid crystal alignment (or,synonymously orientation) structures of the invention comprise asubstrate onto which there is coated a layer of lyotropic liquid crystalmaterial having an ordered molecular structure. The lyotropic liquidcrystal materials may be easily ordered, for example, by the applicationof shear force to the materials, such as occurs during coating of thematerials out of aqueous solution. For sufficient applied shear, theliquid crystalline material can assume an ordered orientation that, upondrying, provides an orientation or alignment substrate useful to orientbulk liquid crystal material in a liquid crystal cell or useful to alignor order a non-liquid crystal coating. Because the levels of shearstress created during orientation of the lyotropic liquid crystalmaterial are low compared to the shear stresses that might causemechanical deformation of the substrates onto which the material isapplied, the process of forming the alignment structures of theinvention has a reduced tendency to create stresses that might distortthe optical properties of the substrate. For certain applications, thealignment or orientation configurations of the invention allow for theuse of more flexible substrates without regard to the degrading ofoptical properties.

Any lyotropic liquid crystal material that forms an ordered structurewhen applied to a suitable substrate can be employed in the invention.Useful lyotropic materials thus include those that form a variety ofordered structures upon application, including crystalline structures,lyotropic films, and other molecular orderings. Typically, the mostuseful lyotropic liquid crystal materials will be those nematic liquidcrystal materials that contain at least one triazine group, includingthose of the type disclosed in U.S. Pat. No. 5,948,487, the disclosureof which is incorporated herein by reference. Preferably, the lyotropicliquid crystal materials are colorless. One class of particularly usefullyotropic materials are those known as “chromonics.” See, e.g., Attwood,T. K., and Lydon, J. E., 1984, Molec. Crystals liq. Crystals, 108, 349.Chromonics are large, multi-ring molecules typically characterized bythe presence of a hydrophobic core surrounded by various hydrophilicgroups. The hydrophobic core can contain aromatic and/or non-aromaticrings. When in solution (typically above about 5 percent by weight ofsolution), these chromonic molecules tend to aggregate into a nematicordering characterized by a long range order. Representative ofchromonic compounds are the following:

(4-Dimethylamino-1-[4,6-di(4-carboxyphenylamino)-1,3,5-triazin-2-yl]pyridiumsulfate) and

(4,6-di(4-carboxyphenylamino)-1,3,5-triazin-2-yl]pyridium sulfate)

Useful chromonic materials are also available in zwitterionic form,among them those of the formulae:

In reference to both formulae C and D above, R¹ is a hydrophilic group,including those generally selected from, but not limited to, carboxylate(COO⁻), sulfonate (SO₃ ⁻), sulfinate (SO₂ ⁻), and phosphate (PO₃H⁻)groups. Preferably, R¹ is a carboxylate or sulfonate group, mostpreferably a carboxylate group. The most preferred location for R¹ ispara with respect to the amino linkage to the triazine backbone of thecompound (shown by Formula C).

R² is a hydrophilic group generally selected from but not limited tocarboxylic acid (COOH), sulfonic acid (SO₃H), sulfinic acid (SO₂H),phosphoric acid (PO₃H), or sulfonamide (SO₂NH₂) groups. Preferably, R²is a carboxylic acid group or a sulfonic acid group, most preferably acarboxylic acid group. The most preferred location for R² is para withrespect to the amino linkage to the triazine backbone of the compound(shown by Formula C).

R³, each of which may be the same or different, is selected from anyelectron donating group, electron withdrawing group or electron neutralgroup. Preferably, R³ is hydrogen or a substituted or unsubstitutedalkyl group, most preferably hydrogen.

R⁴ is generally selected from substituted and unsubstituted positivelycharged heteroaromatic rings linked to the triazine backbone through anitrogen atom within the ring of the R⁴ group. R⁴ can be, but is notlimited to, heteroaromatic rings derived from pyridine, pyridazine,pyrimidine, pyrazine, imidazole, oxazole, thiazole, oxadiazole,thiadiazole, pyrazole, triazole, triazine, quinoline, and isoquinoline.Preferably, R⁴ is a pyridine ring. When present, a substituent for theheteroaromatic ring R⁴ may be selected to determine the properties ofthe chromonic material, for example, a desired color for the alignedlyotropic liquid crystal material. Such substituents for R⁴ may beselected from, but are not limited to, any of the following substitutedand unsubstituted groups: alkyl, carboxyl, amino, alkoxy, thio, cyano,amide and ester. Preferably, when present, the R⁴ substituent is asubstituted amino or pyrrolidino group, more preferably an alkylsubstituted amino group, most preferably a dimethylamio group. Mostpreferably, the substituent is located at the 4 position on a pyridinering.

In some cases, the performance of the lyotropic liquid crystal materialscan be enhanced with the incorporation of one or more additivecompounds. One useful additive is dimethylamino pyridine (“DMAP”), whichwhen added to the lyotropic liquid crystal material in amounts betweenabout 1 and 5 percent by weight (more preferably between about 1 and 2weight percent) improves the optical clarity of the liquid crystalmaterial. Other useful additives include simple sugars, e.g., sucrose,glucose and fructose, which can be added in similar concentrations.Depending on the methods employed to make devices incorporating thealignment structures of the invention, relatively temperature-stableadditive materials (e.g., DMAP) may be preferred.

Layers of these and other chromonic molecules dried from shear coatedsolutions show a self-organized surface structure that easily anduniformly orient liquid crystals or non-liquid crystal coatings in aplanar configuration. FIG. 1, for example, shows a scanning electronmicroscopic image of the surface of a polymeric substrate (polyethyleneterephthalate) shear coated with a layer of Compound A above.

Coating of the liquid crystalline materials can be preformed by anyconvenient means that provides for the ordered arrangement of the liquidcrystals along the plane of the substrate onto which they are applied.Typically, coating methods that impart shear stress to the coatingmaterial during the coating process will be preferred since shear stressimparted during coating can serve to form large and uniform domains ofthe ordered lyotropic liquid crystal molecules. Coating techniques thatimpart such shear stresses include wire-wound rod coating andconventional extrusion dye coating.

Drying of the coated liquid crystalline layer can be performed using anymeans suitable for drying aqueous coatings. Useful drying methods willnot damage the coating or significantly disrupt any molecular orderingof the coated layer imparted by shear stress or other ordering effectsapplied during coating or application.

Substrates onto which the lyotropic materials can be applied include anysolid material that will accept the coating of the liquid crystalmaterial and that possesses whatever optical characteristics may bedesired for its intended application. For example, transparency,translucency or reflectivity may be indicated for a given application.Suitable substrate materials include, for example, glass, rigidpolymeric materials, flexible polymeric films, multilayer films andoptical stacks. In addition to the layer of liquid crystal material, thesubstrates can also include any other layers customarily found indisplay devices or other components useful in displays. Such additionallayers include, for example, polarizers, retarders, color filters, blackmatrices and electronically-addressable active or passive devices (e.g.,transparent electrodes, organic and inorganic light emitting devices andthin film transistors) and the like. Thus, useful substrates can includeone or more optically active layers (such as polarizers, color filters,etc.) and/or one or more additional layers or materials that can be usedto affect or control the transmission, reflection, or absorption oflight through an overall display construction. Suitable substratematerials can be colored or clear and can be birefringement ornon-birefringement.

In representative embodiments, the alignment lyotropic liquid crystalmaterials can be coated or otherwise ordered onto substrates that havepatterned electrodes (e.g., transparent conductive oxide stripes such asindium tin oxide (“ITO”)) and/or that have a matrix of thin filmtransistors (“TFTs”) or other electrically active devices. Suchembodiments would include coating or ordering of the lyotropic materialsdirectly on top of such electrodes or TFTs, on top of one or moreimmediate layers such as one or more planarization layer, or on asurface of the substrate opposing the surface having the electrodes orTFTs. Alternatively, the lyotropic materials can be coated ontosubstrates that are later equipped with electrodes and/or activedevices.

Coating solutions of the lyotropic materials can be made by preparing asimple aqueous solution of water and a pH-adjusting compound such asNH₄OH. The coating solution can then be prepared by dissolving thelyotropic material in aqueous solution along with other additives suchas surfactants and one or more polarizing and/or filtering dyes.Suitable water-soluble polymeric binders can also be added in smallamounts to the solutions in amounts ranging from less than about 1percent by weight to 5 percent or more. Polymers found useful for thispurpose include dextran-type polymers and their sulfates and sulfonatedpolystyrenes. Generally, the liquid crystal materials can be added inamounts sufficient to form a solution of the lyotropic material with aconcentration in the range from about 8 to about 20 percent by weight ofsolution, though concentrations in the range from about 10 to about 16percent are more often preferred. Solutions of the lyotropic materialoutside this concentration range can also be used provided a desiredlevel of functionality is preserved. For example, a solution of thelyotropic material should provide sufficient levels of ordered materialon the final substrate and should therefore be sufficiently concentratedto provide adequate coating thickness and dryability, but not soconcentrated as to be prohibitively difficult to coat and/or orient.

In some cases, it may be particularly desirable to incorporate one ormore color dyes directly into the alignment structure to providepolarizing and/or color filtration functions. Such incorporation caneliminate the need for additional, separate polarizers or color filterlayers in an overall display construction. For example, one or morepleochroic dyes can be incorporated into the ordered matrix of thelyotropic material to provide an ordered color polarizer. Theincorporated dyes can be selected to provide a variety of usefulfiltration and polarizing optical effects in a display construction.Many such constructions are provided in co-pending U.S. patentapplication Ser. No. 09/426,288, the disclosure of which is herebywholly incorporated by reference.

The accompanying drawings illustrate various embodiments of thealignment structures of the invention. FIG. 2, for example, shows theconstruction of a simple liquid crystal cell 200 according to oneembodiment of the invention. The liquid crystal cell 200 includes a topsubstrate 202 and a bottom substrate 206. On at least one surface ofeach substrate is an ordered layer of lyotropic liquid crystal material.Between the top and bottom alignment layers is a layer of aligned liquidcrystal material 204. The aligned liquid crystal material could includeany conventional nematic or smectic liquid crystal material, includingtwisted nematic liquid crystals, super twisted nematic liquid crystals,ferroelectric liquid crystals, anti-ferroelectric liquid crystals,cholesteric materials, etc. The aligned liquid crystal material can alsoconstitute or include any of the chromonic materials or other lyotropicliquid crystal materials described above.

The top and bottom substrates are positioned such that the surfacecontaining the ordered layer of lyotropic material of each of thesubstrates is in contact with the liquid crystal material 204 and arepositioned to orient the liquid crystal material 204 in a desiredmanner. Either or both of the top and bottom substrates 202 and 206 canoptionally include additional optically active layers. For example, inone embodiment, one or more pleochroic dyes are incorporated intolyotropic liquid crystal material of the alignment layer in such amanner that, upon application to the alignment substrate, the pleochroicdye is oriented with the lyotropic liquid crystal and the resultingalignment substrate may also be used as a dichroic polarizer.

FIG. 3 shows one possible construction of an alignment structureaccording to the invention. On substrate 300 there is coated atransparent electrode layer 304 such as indium tin oxide. Adjacent tothe electrode layer 304 is an ordered layer of lyotropic liquid crystalmaterial 306. In one embodiment the lyotropic material includes one ormore pleochroic dyes and can thus function simultaneously, depending onthe selection and orientation of the dye, as a polarizer, a color filterand an alignment layer.

FIG. 4 provides a cross-sectional view of a possible two-polarizerliquid crystal display device, or LCD. The LCD 400 includes a toppolarizer 402, an optional retarder or compensator 404, a liquid crystalcell that includes a top substrate 406, a bottom substrate 410 and aliquid crystal material 408 disposed therebetween. Below the liquidcrystal cell is a bottom polarizer 412 and an optional reflective layeror transflector 414. At least one of the top and bottom substratescontains an ordered layer of lyotropic liquid crystal material disposedalong the surface that is in contact with the liquid crystal material408. The reflective or transflector layer 414 can be provided to allowlighting of the liquid crystal display 400 using ambient light or lightfrom a front light guide (not shown). Optionally, a back light (also notshown) can be placed behind the display to allow for back lighting withor without the optional reflective or transflective layer 414.

FIG. 5 provides a cross-section view of a possible configuration of acolor liquid crystal display device that incorporates one or more of thealignment structures of the invention. The color liquid crystal displaydevice 500 includes a top polarizer 502 and a bottom polarizer 516.Between the top and bottom polarizers is a liquid crystal cell thatincludes a top alignment layer comprising a top substrate material 504on which is disposed an ordered layer or coating of a lyotropic liquidcrystal material 506. A bottom substrate is made of another orderedlayer or coating of lyotropic liquid crystal material 510, a colorfilter array 512 and a bottom substrate material 514. Disposed betweenthe two substrates and in contact with the two adjacent ordered layersor coatings of lyotropic material is liquid crystal material 508.Commonly, full color displays employ a regular pattern of primary colorfilters for color filter array 612. For example, the color filters canbe a regular array of three colors, typically red, green and blue, orcyan, magenta and yellow. The color filters can be colored polarizers.

The following example is offered to aid in the understanding of thepresent invention and is not to be construed as limiting the scopethereof. Unless otherwise indicated, all parts and percentages are byweight.

EXAMPLES Example 1

A chromonic material in zwitterionic form,4-({4-[(4-carboxylphenyl)amnino]-6-[4-(dimethylamino)pyridinium-1-yl]-1,3,5-triazin-2-yl}amino)benzoate,was prepared in the following manner according to the followingreaction.

To a 500 mL three necked round bottom flask with a thermometer, overheadstirrer, and condenser was added 50 grams of4,4-[(6-chloro-1,3,5-triazine,2,4-diyl)diimino]bis-benzoic acid, 15.83grams of 4-dimethylaminopyridine, and 270 mLs of dimethylsulfoxide. Themixture was heated to 90° C. for a total of three hours. The mixture wascooled to room temperature and the resulting solid was collected byfiltration, washed with dimethylsulfoxide and acetone and air dried togive 41.10 grams of1-{4,6-bis[4-carboxyphenyl)amino]-1,3,5-triazin-2-yl}-4-(dimethylamino)pyridiniumchloride. Fourteen grams of this solid was added to a one liter threenecked round bottom flask with an overhead stirrer and to this was added307 mLs of distilled water and 5.53 grams of 28 wt % aqueous ammoniumhydroxide solution. The mixture was stirred until the solid dissolved.The solution was passed down a 600 mm by 58 mm column containing 300 gof Mitsubishi SAT-10 ion exchange resin (the resin was prewashed with a0.5 wt % aqueous ammonium hydroxide solution). The eluent was strippedin vacuum at 15 mm Hg and 80° C. to give 12.66 g of4-({4-[(4-carboxylphenyl)amino]-6-[4-(dimethylamino)pyridinium-1-yl]-1,3,5-triazin-2-yl}amino)benzoate.

Example 2

An aqueous solution of a chromonic compound (Compound A) was preparedhaving a concentration of between 8 and 10 percent by weight ofsolution. A thin layer of the chromonic solution was coated onto oneside of each of two glass slides using a simple knife coater. The twoglass slides were previously coated with a transparent conductive layerof indium tin oxide (700 Å). The slides were air dried, and glass beads5 g in diameter were sprayed from solution on the side of each slidecoated with the chromonic layer. The slides were adhered together insuch a manner that the coating directions of the chromonic layers wereat 90° to one another and such that the two cells together formed asimple cell construction. A small opening was left between the slides,and the cell was vacuum filled with nematic liquid crystal materialZLI1565, available from Merck Inc.

The filled cell was viewed under microscope between two crossedpolarizers. The filled cell transmitted substantially all light betweenthe polarizers, indicating the achievement of a uniformly-aligned 90°twist of the nematic liquid crystal material within the cell.

Various modifications and alterations of this invention will be apparentto those skilled in the art without departing from the scope and spiritof this invention, and it should be understood that this invention isnot limited to the illustrative embodiments set forth herein.

What is claimed is:
 1. An alignment structure comprising: a substratehaving disposed thereon an oriented layer of a colorless, nonpolymeric,lyotropic liquid crystal material; and liquid crystal material disposedon the oriented layer and aligned by the oriented layer.
 2. Thealignment structure of claim 1 wherein said lyotropic liquid crystalmaterial comprises a nematic or smectic liquid crystal material.
 3. Thealignment structure of claim 1 wherein said lyotropic liquid crystalmaterial comprises a chromonic material.
 4. The alignment structure ofclaim 3 wherein said chromoic material is selected from the groupconsisting of(4-Dimethylamino-1-[4,6-di(4-carboxyphenylamino)-1,3,5-triazin-2-yl]pyridiumsulfate and 4,6-di(4-carboxyphenlamino)-1,3,5-triazin-2-yl]pyridiumsulfate.
 5. The alignment structure of claim 1 wherein said orientedlayer of lyotropic liquid crystal material comprises a crystallinestructure.
 6. The alignment structure of claim 1 wherein said orientedlayer of lyotropic liquid crystal material comprises a lytropic film. 7.The alignment structure of claim 1 wherein said lyotropic liquid crystalmaterial comprises at least one triazine group.
 8. The alignmentstructure of claim 1 wherein said lyotropic liquid crystal materialcomprises a hydrophobic core surrounded by at least one hydrophilicgroup.
 9. The alignment structure of claim 1 further comprising one ormore additives.
 10. The alignment structure of claim 9 wherein theadditive is dimethylamino pyridine.
 11. The alignment structure of claim9 wherein the additive is a simple sugar.
 12. The alignment structure ofclaim 9 wherein the additive is present in an amount between about 1 andabout 5 percent by weight.
 13. The alignment structure of claim 1further comprising one or more pleochroic dyes.
 14. The alignmentstructure of claim 1 further comprising a transparent electrode layer.15. The alignment structure of claim 1 further comprising at least onecolor filter element or array.
 16. The alignment structure of claim 1further comprising at least one additional layer in contact with theordered layer of lyotropic liquid crystalline material.
 17. Thealignment structure of claim 16 wherein said additional layer comprisesa cholesteric material.
 18. The alignment structure of claim 16 whereinsaid additional layer comprises a polymer film.
 19. The alignmentstructure of claim 1 wherein said substrate is a glass substrate. 20.The alignment structure of claim 1 wherein said substrate comprises atransparent material.
 21. The alignment structure of claim 20 whereinsaid transparent material comprises a polyimide.
 22. The alignmentstructure of claim 1 wherein said substrate comprises a reflectivematerial.